Color pixels used in color displays are typically formed of three light sources, or subpixels, each emitting light of a different wavelength. Typically, one subpixel emits red light, one subpixel emits green light, and one subpixel emits blue light. The apparent color of the pixel depends on the relative intensities of the three colors. The apparent color is determined by the current applied to each of the three subpixels.
Packaging the subpixels into the pixels of a display is complex and costly. Light-emitting diodes are commonly used as subpixels. The light-emitting diodes of the subpixels are each formed from different semiconductor materials, so the individual light-emitting diodes of the subpixels cannot be combined. The size of pixels must be less than the resolution of the human eye to prevent the observer from discerning the individual pixels. The subpixels must be smaller than the individual pixel to fit within the individual pixel. Each subpixel typically also includes associated electronics to enable the subpixel to be individually addressable.
Use of subpixels emitting light at a particular wavelength also causes problems with color quality as the display ages. As light-emitting diodes age, the intensity emitted for a given applied current changes. Red, green, and blue light-emitting diodes typically age at different rates. Because the apparent color of the pixel depends on the relative intensities of the three colors and the intensity of the three light-emitting diodes shifts with time, the apparent color for a given relative current profile will shift over time.